Need help choosing a Crossfire MB

With what you listed ASUS Crosshair IV Formula. You do NOT want a MOBO with on-board GPU.

RAM - http://www.corsair.com/products/phenomii/default.aspx
However, the 6-core AMDs have a different Memory Controller and allow up to 2000 MHz RAM; it depends on how high you plan to OC; if moderate to none then stick with the 1600 MHz RAM.

I'm building {ASUS Crosshair IV Extreme} using G.SKILL Flare Series 8GB (2 x 4GB) DDR3 2000 (PC3 16000) F3-16000CL9D-8GBFL http://www.newegg.com/Product/Product.aspx?Item=N82E168...

MOBOs Side-by-side - http://www.newegg.com/Product/Productcompare.aspx?Submi...|13-131-655^13-131-655-TS,13-131-644^13-131-644-TS,13-131-667^13-131-667-TS

I intend to do no OC (since I'm a complete 0 at it).
In what way would a board with onboard gpu be a bad thing? Because, apart from that, the ASUS M4A89GTD PRO/USB3 on the comparison you linked me seems to be more than enough for me.

Thanks for your help!

Problems: 1. Shared Bandwidth with you GPUs, 2. Shared Memory from your RAM. At best you can Disable the on-board GPU in both the BIOS and Device Manager, but it 'may' only solve the RAM issue, but not the Bandwidth issue. {No, it doesn't matter if the on-board just sits there - it's an Integrated component ~ a vestigial organ}

You need a 'Balance' system and Components; I would never run CF HD 6870's with a cheaper 'sharing' MOBO; it's unbalanced and you'll loose some of the performance of your CF. Other than that -- it's your rig.